perplexed by our pressure assist toilets

We recently moved into a house with 2 pressure assist toilets (American Standard). I've never seen these before, so I'm a little confused about how they work and how to fix them...

The first problem was that the flush on both toilets was really half-hearted. The flappers would shut after only about 1/3 of the tank had drained. To solve this, I adjusted the floats above the flappers (moving them from mid-way along the chain to right down on top of the flappers), and shortened the chains. This seemed to do the trick, and the flushes were a lot better since the flappers stayed open longer.

Now, I've noticed that the toilets hiss continuously (and occasionally make trickling noises). It's a really quiet hiss, but it looks like a small amount of water is always running down the inside of the overflow tube. Did I make the flappers so buoyant that they're no making a firm seal anymore? Or is this another issue?

If the flapper is being held up by the chain, you are constantly dumping water, and be on the lookout for a surprise when you get your water/sewer bill, it could be huge.

Modern toilets usually do not empty themselves with each flush (the tank, the bowl should!) - they use that height to generate a more forceful flush. Think of a water tower on top of a hill - you get the pressure from the height.

On a pressure assist toilet, the water goes into a closed tank with a bladder in it and captive air. The water pressure pushes the water into the tank, compressing the captive air. When you flush, instead of gravity pushing the water out for the flush, it is the stored energy from the captive air (compressed by the water pressure) pushing it out. Thus, the water pressure from the supply is 'assisting' the water flow and the resulting flush.

If you have a typical flapper valve, it doesn't sound like it is a pressure assist toilet.

The static water height in the tank needs to be high enough to get the proper 'head' in a gravity flush; if it is too low, the water doesn't have as much pressure.

Thanks for the reply and sorry for the confusion (plumbing is clearly not something I understand)...

I thought that it was a pressure assist toilet because it didn't have a float and had a little yellow tank instead, but my new theory is that it's one of these American Standard Smart Valve 2000 fill valves:

My sister had in her previous home an American-Standard "New Cadet" which she picked out herself at HD. It came with the yellow "Smart Valve". It was probably a year later when my father called me and in very angry tones asked me to come the next day and put a "proper float valve" in my sister's new toilet because my brother-in-law fooled with the Smart Valve so it wouldn't shut off (since reading the comments about the Smart Valve, I doubt he touched it at all), and it ran the well dry and nearly burned out the bump (she burned out at least 2 pumps in that house).

I went up the next day and in about 15 minutes installed a Fluidmaster 400A, thus soothing the nerves of my father and my sister.

That toilet leaked later on from the tank to bowl bolts. They were not installed right (too loose) and one of them had rusted so badly that I had to use a hack saw to remove it!!! I replaced the bolts (making sure the new ones were brass), washers, and the tank to bowl gasket.

I am using Fluidmaster 400A and Korky Quiet Fill. On a restoration of an antique tank, I occasionally use the Mansfield 09 (for the sound effects), but readily agree that the new styles are more trouble free as well as practical, because they signal you when there is a slow leak in the flapper by turning themselves on for a few seconds.